This application relates generally to apparatus and method for applying filter material to continuous lengths of drainage tubing, and more specifically, to apparatus and method for applying such filter material to the drainage tubing as it is being installed in the ground.
Water drainage systems have a long history of use in cultivated agricultural areas and in residential developments for collecting and removing excess water from the soil. Typically, such drainage systems have comprised networks of clay or concrete tiles placed in open trenches which are then carefully back-filled. Importantly, the tiles are perforated or slightly spaced to allow excess ground water to seep into the tile network to be carried thereby away from the drained soil. The required steps of trench digging and back-filling, and of carefully laying individual tiles in the trench, are time-consuming and tedious tasks. For this reason, conventional drainage tiles have to a large degree given way to more modern and convenient drainage conductors such as continuous lengths of flexible plastic tubing. For example, U.S. Pat. Nos. 3,374,634 and 3,699,684 show flexible plastic tubing which is corrugated for flexibility and high strength and has spaced openings to admit ground water. Such plastic tubing is advantageous in that it is lightweight and long-lasting and can be quickly and easily laid in continuous lengths and does not use short lengths which are easily dislodged during trench back-filling, as occurs with tile. Further, the continuous lengths of plastic tubing are especially suitable for use with modern trenching and laying equipment which continuously and simultaneously digs a trench and lays the drainage tubing, and may also back-fill the trench. Such tubing is also especially suitable for use with what may be termed "closed" trench laying in which a sturdy plow blade and boot forms a slot and lays the tubing without actually excavating a trench.
A major problem with many underground drainage systems is that the drainage collectors tend to become clogged with sediment or silt carried into them by the water. This is especially the case when the drainage tubing is placed in soil composed of fine, loosely packed particles such as fine sand or other light topsoil. A particular drainage field may contain some areas where silting occurs and others where it does not tend to occur, as in natural beds of gravel. In the past, the sediment or "silting" problem has been attacked by laying a bed of gravel about selected portions of the drainage collectors so as to provide a rough filter between light soil and the collector. This procedure has not been totally satisfactory, however, because the gravel also tends to become clogged, and because the time and material needed to lay the gravel bed is economically prohibitive. Further, a gravel-bed filter is totally incompatible with modern drain-tube installing equipment which continuously and simultaneously forms a trench or slot in the ground and lays drainage collectors therein.
In more recent efforts to overcome the silting problem, various other filter materials and systems for applying them to drainage tubing have been proposed. These include, for example, wrap-around filters of porous mats formed from straw or coconut fibers and wraps and sleeves of filter cloth such as woven fabric of nylon or other plastics, non-woven fabrics or polyester, etc. Such filters are typically applied to the tubing under factory conditions of an industrial plant away from a drain-laying job site, and the filter-covered conduit is transported to the job site for installation. Alternately, these filter materials are sometimes applied to drainage conduit after it is placed in an open trench. Both of these methods have serious drawbacks. For example, applying the filter to the conduit away from the job site subjects the filter to damage during handling and transport, and does not readily permit filter to be applied at only those portions of the drainage field where it is required and omitted elsewhere. Similarly, placing the filter about the tubing after the tubing is in the ground is slow and laborious, and may require the tubing to be suspended in the trench as the filter is placed about it. This procedure also involves the danger of damage to the filter and of leaving gaps in the filter covering. Further, the "in the ground" filter placement is impossible with modern trenching and laying equipment since the filter must be applied by hand in an open trench.
The present invention provides apparatus and a method for applying a tubular filter sleeve to continuous lengths of drainage tubing as such tubing is being laid with mechanized equipment, without subjecting the filter to damage from handling or transporting filter-covered conduit. It allows convenient application of the filter about continuous lengths of tubing where it is desired and omission of the filter from the tubing where it is not required. Further, the invention provides for installing filter without substantially increasing installation time of a drainage system, and is compatible with modern mechanized trenching and laying equipment, and is easy to use and economically feasible.